CN117236141B - Foundation deformation calculation method based on numerical model stress extraction - Google Patents
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Abstract
The invention discloses a foundation deformation calculation method based on numerical model stress extraction, which comprises the steps of firstly establishing a numerical model to calculate the vertical and horizontal additional stress distribution of foundation soil, wherein the elastic modulus of the foundation soil is selected in the range of 2-5 times of the compression modulus according to engineering experience; adopting a layered sum method, directly calculating layered settlement for a natural foundation, respectively calculating settlement of a reinforced area and a lower horizontal layer for a composite foundation, superposing the layered settlement and multiplying the layered settlement by a settlement experience correction coefficient to obtain the final settlement; the projection of the horizontal displacement calculation point on the ground and the vertical column below the projection are regarded as limited elastic long beams which are vertically placed, the cross section of the column is square, the side length of the column is preferably 0.1m or less, the modulus of the beam is identical to that of the soil, one end of the beam is positioned on the ground surface plane, the other end of the beam is positioned on the plane where the calculation depth is positioned, the distributed load is dispersed into a plurality of concentrated loads, the foundation bed coefficient is determined according to the specification, and the horizontal displacement of the calculation point is obtained through a method of the elastic foundation beam.
Description
Technical Field
The invention relates to the field of foundation deformation monitoring, in particular to a foundation deformation calculation method based on numerical model stress extraction.
Background
The foundation design is an important ring in the field of civil engineering, and the calculation of the vertical settlement and horizontal displacement of the foundation is an important component in the foundation design.
In the aspect of vertical settlement calculation, the method with the highest acceptance is a layering summation method, and can be used for calculating a natural foundation or a composite foundation of stratum layering distribution. The key points are whether the soil property parameters are selected reasonably or not and whether the calculation of the additional stress is accurate or not.
The soil property parameter most closely related to sedimentation is the modulus of the soil, the most commonly provided modulus in the geological report is the compression modulus under different pressure sections, the modulus which is most easily obtained from the field or indoor test, the displacement rate composite modulus method and the bearing ratio composite modulus method are both composite foundation modulus estimation based on the compression modulus, and the compression modulus is adopted in the layered sum method formula. In practical engineering, therefore, deformation calculation makes it difficult to bypass the compression modulus.
The additional stress calculation methods suggested in the building and roadbed design specifications mainly comprise a Boussinesq method, a Mindlin method, an equivalent entity method, an L/3 method, a stress diffusion method and the like. Wherein: the first two methods have more perfect theoretical basis, but the Boussinesq method is mostly suitable for homogeneous foundations; although the Mindlin method can consider the effect of piles, the calculation is complex, and programming solution is needed in many cases. The latter three methods are simple and convenient to calculate, but because of the experimental algorithm, the designer has great influence on the calculation result in terms of the value of the parameter, the simplification of the working condition and the selection of the calculation method. The selection of a settlement calculation theoretical frame and soil parameters is widely accepted according to the technical route recommended by the current specification, but the additional stress calculation is complex for a structural foundation with a complex structural form or a composite foundation through piling, and formulas can not be applied under many working conditions. Therefore, a calculation method of additional stress under complex working conditions which is suitable for a layering summation method and a compression modulus is needed to be found, and a complete settlement calculation method is formed by the three methods.
Besides the calculation method recommended by the specification, in engineering practice, deformation calculation of special work points often uses numerical simulation software such as finite elements or finite difference, and the like, and the deformation calculation is widely used and accepted in a perfect theoretical system and with strong calculation capability. The numerical modeling mostly uses the elastic modulus of the soil, various physical and mechanical parameters of the soil can be obtained through complex indoor tests in scientific research work, but the elastic modulus is not directly reflected through a geological report, and is generally obtained through conversion of multiplying the compression modulus by a coefficient which is 2 to 5 times, the coefficient has a wider value range, does not have unified execution standard, and is greatly affected by experience. The deformation obtained by numerical simulation is changed greatly due to the multiplied change of the elastic modulus, so that many designers often only refer to the stress distribution and deformation trend obtained by numerical simulation, and doubt attitude is kept on the specific numerical value of the deformation, which also limits the popularization and application of numerical simulation software in the design process.
In the aspect of vertical settlement calculation, a plurality of choices are given in the specification, but a specific horizontal displacement calculation method is not given in the specification, and in engineering practice, calculation is generally carried out through numerical simulation, but calculation differences caused by different elastic modulus and poisson ratio values of different designers cannot be avoided.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides a method for calculating vertical settlement and horizontal displacement of a natural foundation or a composite foundation, which has high accuracy and low calculation difficulty and is suitable for various working conditions.
For this purpose, the invention adopts the following technical scheme:
a foundation deformation calculation method based on numerical model stress extraction comprises the following steps:
s1, establishing a numerical simulation model according to an on-site working point:
establishing a numerical simulation model by using soil parameters directly acquired from a geological survey report; after material attribute setting, load setting, contact setting and boundary setting are carried out in the model, shielding units except for foundation soil by a method of a dead unit to obtain a foundation model;
s2, extracting horizontal and vertical additional stress distribution of the foundation:
the ground stress distribution under the dead weight load is calculated through a static general analysis step, and the calculated ground stress distribution is led into a foundation model obtained in S1 through an ODB file leading method to perform ground stress balance;
when the site foundation is a natural foundation, activating the embankment and the external load on the embankment in the model after the ground stress is balanced;
when the site foundation is a composite foundation, firstly activating a pile, a cushion layer or a concrete slab structure in a model after the ground stress is balanced, then carrying out ground stress balance again, and finally activating the embankment and the external load on the embankment;
extracting uniform load curve of horizontal additional stress changing along with depth by using model after external load is activatedAnd a vertical additional stress profile with depth;
s3, calculating the vertical settlement of the foundation:
calculating the vertical settlement of the foundation according to the following formulas：
，
In the method, in the process of the invention,the total settlement of the foundation; />Calculating an empirical coefficient for sedimentation;
s4, calculating the horizontal displacement of the foundation:
the method comprises the steps that a vertical earth column of a to-be-measured point below a ground surface projection point is regarded as an elastic foundation beam with a limited length, the cross section of the earth column is square, the side length is smaller than or equal to 0.1m, and a deflection differential equation calculated by a Winker elastic foundation beam theory is used as a basis;
for any position on the elastic foundation beamuUniformly distributed load applied to the position, and the uniformly distributed load is scattered into a plurality of concentrated loads by using a differential principleP(u) calculating the horizontal displacement caused by each of the concentrated loads by：
，
In the method, in the process of the invention,is the flexibility coefficient of the elastic foundation beam, +.>；/>Modulus for elastic foundation beams; />Is the section moment of inertia; />Is the width of the section; />Is the foundation bed coefficient;F 1 ，F 2 ，F 3 ，F 4 as a function of gram Lei Luofu;
；
；
；
；
the horizontal deformation of the point to be measured at the projection point of the ground surface is obtained; />The corner of the projection point of the to-be-measured point on the ground surface is the corner of the projection point of the to-be-measured point on the ground surface; />The bending moment of the point to be measured at the projection point of the ground surface is the bending moment of the point to be measured at the projection point of the ground surface; />The concentrated force of the point to be measured on the projection point of the ground surface is obtained;xandyand the X axis is depth, and the Y axis is horizontal deformation of the elastic foundation beam for the coordinate value of the point on the elastic foundation beam.
Each length direction of the elastic foundation Liang Yanliangm divides a micro-segment into the following formula:
，
in the method, in the process of the invention,uniform load curve obtained for S2 +.>At the position ofuA value at.
Function of displacement of beam with depth caused by each concentrated loadAdding, calculating any position on the beam under the action of uniformly distributed load by the following methodxHorizontal displacement of the part->：
。
When the foundation described in S3 is a natural foundation, the total settlement of the foundation is calculated by the following formula：
，
In the method, in the process of the invention,ncalculating the number of soil layers divided in the depth range for foundation settlement;is the firstiAverage compression modulus of layer soil;is the firstiThe thickness of the layer soil; />Is the first in the natural foundationi Average vertical additional stress of the layer soil.
When the foundation described in S3 is a composite foundation, the total settlement of the foundation is calculated by the following formula：
,
In the method, in the process of the invention,the settlement amount of soil mass in the reinforced area; />Is the settlement of the soil body of the lower lying layer;
order then 1 For the number of soil layers divided in the range of the reinforcement area,n 2 for the number of soil layers divided in the lower lying range,n=n 1 +n 2， the saidObtained by the following formula:
，
in the method, in the process of the invention,is the firsti Average compression modulus of the layer soil; />Is the firsti The thickness of the layer soil; />Is the first in the composite foundationi Average vertical additional stress of the layer soil.
When the composite foundation is a flexible pile composite foundation, the following formula is adopted:
，
in the method, in the process of the invention,for reinforcement zone->The average compression modulus of the layer composite soil body can be calculated by a substitution rate composite modulus method>：
，
，
In the method, in the process of the invention,the replacement rate is the composite foundation area; />Is the area of a single pile; />The area of the soil body unit is compounded around the pile;is the compression modulus of the pile body.
The bearing force ratio and the composite modulus method can also be used for calculating theThere is a formula:
，
，
in the method, in the process of the invention,the foundation is the basic bearing capacity of the natural foundation; />The bearing capacity is allowed for the composite foundation; />To increase the coefficient of load bearing than compression modulus.
When the composite foundation is a rigid pile composite foundation and the differential settlement of pile soil on the surface of the foundation is not negligible, calculating the settlement of the soil body of the reinforced area by a pile body compression methodThere is a formula:
in the method, in the process of the invention,the pile body penetration amount is as follows; />The compression amount of the pile body is obtained by the following formula:
，
in the method, in the process of the invention,the pile length is the pile length; />The modulus of the pile body obtained in the step S1; />The vertical additional stress is a change curve of the vertical additional stress along with the depth, and is obtained through S2 calculation; z is the depth of the pile body.
When the composite foundation is a rigid pile composite foundation and differential settlement of pile soil on the surface of the foundation is negligible, calculating the vertical settlement of the foundation by using a Mindlin methods。
Preferably, in S4, the cross section of the soil column is square, and the side length of the square is less than or equal to 0.1m;less than or equal to 0.1m; pending parameter->，/>，/>，/>Determined by known loading conditions and boundary conditions.
Preferably, the boundary in the step S1 is set to limit the horizontal displacement of the boundary surface around the model to zero and limit the vertical displacement of the bottom boundary to zero; the load in S1 is set to be downward gravity acceleration and other additional loads (such as rail, vehicle, canopy column, adjacent structure load and the like); the soil property parameters comprise the gravity, the elastic modulus, the cohesive force and the internal friction angle, and the elastic modulus value is in the range of 2-5 times of the compression modulus according to engineering experience.
Research shows that in finite element or finite difference calculation of foundation settlement, the change of elastic modulus in a reasonable range can influence the settlement calculation result, but the influence on the result of additional stress is small, namely the calculation result of the additional stress is reliable no matter whether the elastic modulus of soil is 2 times or 5 times of the compression modulus. Similar to vertical sedimentation, the invention is based on the fact that the value of the elastic modulus and the poisson ratio has a larger influence on horizontal displacement and a smaller influence on horizontal additional stress.
Compared with the prior art, the invention has the following beneficial effects:
1. the method adopts compression modulus, calculates vertical additional stress by using a numerical model, and calculates vertical settlement by combining a standard algorithm; and taking the soil column with the horizontal displacement calculation point as a limited long beam which is vertically placed, extracting horizontal additional stress distribution of the side surface of the soil column through numerical simulation, and calculating the horizontal displacement through a method of an elastic foundation beam. The method can calculate complex working conditions, and has more common execution standard and higher acceptance;
2. the method avoids the defect of overlarge deformation calculation result difference caused by different elastic modulus values due to manual work in numerical simulation;
3. all calculation parameters required by the method can be obtained through a geological survey report or a normative table lookup;
4. the method reduces the calculation difficulty, does not need programming calculation, and can acquire the additional stress through numerical simulation of commercial software;
5. the method has wide application range, and is suitable for not only natural foundations, but also composite foundations such as pile nets, pile rafts, pile plates and the like; the method is not only suitable for building foundations, but also suitable for highway and railway roadbeds; and is also suitable for the working condition with adjacent structures and auxiliary structures.
Drawings
FIG. 1 is a schematic flow chart of the calculation method of the present invention;
FIG. 2 is a schematic diagram of a finite element model of a railway double-track subgrade constructed in accordance with an embodiment of the present invention;
FIG. 3 is a finite element model schematic of a pile structure;
FIG. 4 is a schematic diagram of a calculation point position in an embodiment;
FIG. 5 is a vertical additional stress profile in embodiment one;
FIG. 6 is a horizontal additional stress profile for example one;
fig. 7 is a schematic view of a winker elastic foundation beam calculation.
Detailed Description
The following describes the calculation method of the present invention in detail with reference to the drawings and examples.
Example 1
The case of the composite foundation in the foundation deformation calculation method based on numerical model stress extraction according to the present invention will be described below by taking a railway double-track roadbed composite foundation model as an example.
Referring to fig. 1, the method comprises the steps of:
s1, establishing a numerical simulation model according to an on-site working point:
taking ABAQUS commercial finite element software as an example, a railway double-track roadbed composite foundation model is built according to a certain site working point and reasonable simplification according to engineering experience, and the model is shown in figures 2 and 3.
The width of the top surface of the embankment is 13.6m, the width of the bottom surface of the embankment is 28.6m, the height of the embankment is 5m, the width of the foundation is 88.6m, the depth of the foundation is 50m, and the length of the model along the line direction is 10m. The foundation soil is 3m thick clay (soft plastic), 9m thick mucky clay, 6m thick powdery clay (soft plastic), 2m thick powdery clay (compact), and powdery clay (hard plastic) from top to bottom, the attribute parameters of the foundation soil and other materials are shown in table 1 and table 2 respectively, and the elastic modulus of the foundation soil can be 2-5 times of the compression modulus, and in the example, 2 times of the elastic modulus of the foundation soil.
TABLE 1
| Material name | Bulk density (kN/m) 3 ） | Compression modulus (MPa) | Poisson's ratio | Cohesive force (kPa) | Internal friction angle [ ] o ） |
| Clay (Soft plastic) | 17.5 | 3.1 | 0.35 | 18 | 7 |
| Mucky soil | 18 | 2.9 | 0.38 | 12 | 5 |
| Powdery clay (Soft plastic) | 19.5 | 5.5 | 0.35 | 15 | 7 |
| Pink soil (dense) | 21 | 20 | 0.35 | 27 | 13 |
| Powdery clay (hard plastic) | 20 | 19 | 0.35 | 30 | 12 |
TABLE 2
| Material name | Bulk density (kN/m) 3 ） | Elastic model (MPa) | Poisson's ratio | Cohesive force (kPa) | Internal friction angle [ ] o ） |
| Packing material | 22 | 40 | 0.33 | 5 | 40 |
| Concrete slab | 24 | 31500 | 0.2 | \ | \ |
| Tubular pile | 24 | 38000 | 0.2 | \ | \ |
The underground water level is positioned on the ground surface, and the gravity of the soil is the gravity of floating. The foundation is reinforced by adopting a pile plate structure, the length of the pipe pile is 20m, the diameter of the pipe pile is 0.5m, the distance between the piles is 2.5m, the thickness of a concrete slab is 0.5m, the pile top is bound with the concrete slab, and other parts are in friction contact with each other, so that the friction coefficient is 0.3. The bed coefficients are determined by specification. In the boundary setting, the horizontal displacement of the boundary surface around the limiting model is zero, and the vertical displacement of the bottom boundary surface is limited to be zero. In the load setting, downward gravitational acceleration is applied to the model, and two 54.1kN/m tracks with the width of 3.1m and the size and train load are applied to the top surface of the roadbed. The units outside the foundation are shielded by means of dead units, i.e. by temporarily shielding units in ABAQUS that are not related to a certain analysis step, and activating them when needed.
S2, extracting horizontal and vertical additional stress distribution of the foundation:
based on the composite foundation model established in the step S1, the distribution of the ground stress under the dead weight load is calculated through a static general analysis step, then the ground stress balance is carried out by adopting a method of leading in an ODB file (the ground stress result of the last increment step under the dead weight load is set as initial ground stress, the static calculation is carried out again, the maximum displacement or maximum strain is extracted, if the magnitude of the displacement or the strain meets the calculation precision, the ground stress balance is considered to be completed, otherwise, the steps are repeated.
The pile structures (i.e. piles and concrete slabs) are then activated by means of the dead units and again subjected to ground stress balancing, finally activating the embankment and the external load on the embankment. If there are more components or there are additional structures, the stress balancing and activating unit may be performed as many times as desired.
The method can solve the vertical sedimentation and the horizontal displacement of any position in the foundation, and the example is taken as an example of calculating the vertical sedimentation of the foundation surface below the center of the embankment and the horizontal displacement of the ground surface at the position 5m outside the toe. A data extraction path is set in the ODB file. As shown in fig. 5, a change curve of vertical additional stress caused by the embankment load with depth in the center point (point D in fig. 4) below the embankment and foundation soil below the embankment is extracted, and the additional stress can be obtained by subtracting the stress result before the embankment load is applied from the stress result after the embankment load is applied. If pile body compression method is needed to calculate the settlement of the reinforced area, extracting the change curve of the pile body additional stress along the depth of the pile nearest to the calculation point. According to the principle that the vertical additional stress is equal to 10% of the effective dead weight stress, the calculated depth is determined to be 35m. As shown in fig. 6, a change curve of horizontal additional stress along the depth at 5m outside the toe (point a in fig. 4) and below is extracted, as shown in fig. 6.
S3, calculating vertical settlement of the foundation surface:
according to the design specification of the foundation of the building, the natural foundation settlement can be calculated according to the following formula,
(1)
wherein:
the vertical settlement of the foundation;
the total settlement of the foundation;
calculating an empirical coefficient for sedimentation;
ncalculating the number of soil layers divided in the depth range for foundation settlement;
is the firstiAverage compression modulus of the layer soil;
is the firstiThe thickness of the layer soil;
is the first in the natural foundationiAnd (3) calculating the average vertical additional stress of the layer soil by S2.
For composite foundations, there are:
(2)
wherein,the settlement amount of soil mass in the reinforced area; />Is the settlement of the soil body of the lower lying layer.
Order then 1 For the number of soil layers divided in the range of the reinforcement area,n 2 for the number of soil layers divided in the lower lying rangen=n 1 +n 2 Lower bed sedimentation can be calculated by the following formula:
(3)
in the method, in the process of the invention,is the firsti Average compression modulus of the layer soil; />Is the firsti The soil thickness of the layer; />Is the first in the composite foundationi Average vertical additional stress of the layer soil.
The composite foundation is divided into a flexible pile composite foundation and a rigid pile composite foundation. The rigid pile composite foundation can be divided into two cases according to engineering experience, namely whether differential settlement of pile soil on the surface of the foundation can be ignored.
For the flexible pile composite foundation, the settlement of the reinforced area can be calculated by a substitution rate composite modulus method or a bearing ratio composite modulus method, then the settlement of the lower horizontal layer is calculated by a method (3), and the total settlement is obtained by summing the settlement of the reinforced area and the settlement of the lower horizontal layer. The displacement rate composite modulus method is a general method for calculating the settlement of the flexible pile composite foundation, and if the bearing capacity data of the natural foundation and the composite foundation exist in the field, the bearing capacity ratio composite modulus method can be adopted, and the calculation formulas of the two methods are as follows.
1) Substitution rate complex modulus method:
the average modulus of the composite soil body of each layer of reinforced area is set asE csi The soil settlement of the reinforced areas 1 The method comprises the following steps:
(4)
in the method, in the process of the invention,for the average compression modulus of the first layer composite soil body of the reinforced area, the value can be obtained by an area weighted average method:
(5)
(6)
in the method, in the process of the invention,the replacement rate is the composite foundation area;
is the area of a single pile;
the area of the soil body unit is compounded around the pile;
is the compression modulus of the pile body.
2) Bearing force ratio complex modulus method:
the bearing capacity ratio method is adopted to determine each layer of soil in the reinforced area through modulus increase coefficient of the soil in the reinforced areaE csi ：
(7)
(8)
In the method, in the process of the invention,the foundation is the basic bearing capacity of the natural foundation;
the bearing capacity is allowed for the composite foundation;
to increase the coefficient of load bearing than compression modulus.
For the two cases of the rigid pile composite foundation, the following two methods can be adopted respectively:
1) Pile body compression method:
for the condition that the differential settlement of pile soil on the surface of the foundation (such as a pile-net structure) is not negligible, the pile body compression method can be adopted to calculate the settlement of the reinforced area. The method obtains the compression amount of the reinforced area by calculating the compression amount of the pile body. Setting the penetration of pile body asThe compression of the pile body is ∈>Then the soil body is pressed and settled in the reinforced area of the composite foundations 1 Can be calculated by the following formula:
(9)
the compression of the pile body can be obtained by pile body stress and pile body modulus:
(10)
in the method, in the process of the invention,the pile length is the pile length; />Is the modulus of the pile body; />Is a vertical additional stress variation curve with depth. Wherein, the penetration of the pile body is taken according to the specification, the modulus of the pile body is S1 and +.>Calculated by S2, z is depth.
2) Mindlin method:
for the situation that the differential settlement of pile soil on the foundation surface is negligible (such as pile plate structure in the example), the Mindlin method in the specification can be adopted to calculate the vertical settlement. The Mindlin method in the specification calculates additional stress generated by superposition of pile side and pile end loads in foundation soil through table lookup, and then calculates through a layering summation method. The additional stress calculation is completed in finite elements without table lookup, so that the additional stress extracted in the step S2 is carried into the formula (1) for calculation, similar to a natural foundation, without distinguishing a reinforcing area from an underlying layer. Number of soil layersn70, the soil thickness of each layer0.5 m->From the calculation of S2, the additional settlement of the foundation surface at the center below the embankment was found to be 8.0 cm by the material parameters of tables 1 and 2, fig. 5, and equation (1).
S4, calculating the horizontal displacement of the foundation:
the vertical column at the position 5m (point A) outside the toe and below the toe is regarded as a limited long beam, the length of the beam is 35m, the section is a square with the side length of 0.1m, the soil body outside the column is regarded as a foundation, and the deformation is calculated by applying the Winker elastic foundation beam theory, as shown in figure 7. According to basic assumption of the elastic foundation beam and the deformation coordination conditions of the foundation beam and the soil body under the beam, the stress balance condition of the micro-segment of the elastic foundation beam is considered, and a deflection differential equation is obtained:
(11)
in the method, in the process of the invention,modulus for elastic foundation beams; />Is the section moment of inertia; />Is the width of the section; />Is the foundation bed coefficient;xandythe X-axis is depth, and the Y-axis is horizontal deformation of the elastic foundation beam, which are coordinate values of points on the elastic foundation beam in FIG. 7; />And (3) uniformly distributing the load curve of the horizontal additional stress in S2 along with the change of the depth.
When the elastic foundation beam is at any positionuThe part is uniformly loadedqWhen the arbitrary section on the beam is obtained (the distance from the origin O isxA section of) is:
(12)
wherein:
is the flexibility coefficient of the elastic foundation beam, +.>；
F 1 ，F 2 ，F 3 ，F 4 As a function of gram Lei Luofu;
；
；
；
；
the horizontal deformation of the point A;
is the corner of the point A;
the bending moment of the point A;
the force is concentrated at the point A;
uis the position of the load center point;
c is the position of the end point of one side of the uniform load close to the origin O;
b is the end point of the foundation beam (lying in the calculated depth plane).
However, the integral of the uniformly distributed load in the (12) is difficult to calculate, and the uniformly distributed load is scattered into a plurality of concentrated loads by the principle of differentiationPAnd (u) finally, superposing the action effects of the loads. The displacement caused by each concentrated load is:
(13)
each micro-segment is divided into not more than 0.1m along the length direction of the beam. Taking a micro-segment of 0.1m as an example, the horizontal additional stress to the beam can be 350 concentrated loads due to the length of the beam being 35mP(u):
(14)
Wherein:
for uniformly distributing load curve->At the position ofuA value at.
Assuming that constraint conditions at two ends of the beam are free, determining undetermined parameters through known load conditions and boundary conditions，，/>，/>. Four parameters are brought into the formula (13), so that displacement caused by each concentrated load can be overlapped through the formula (15), and any position on the beam under the action of uniformly distributed load can be obtainedxDisplacement of the parts, e.g. of the orderxZero, resulting in a surface horizontal displacement of 6.5 cm.
(15)
According to the on-site monitoring result, the vertical settlement of the surface of the central foundation of the post-construction roadbed is 8.6 cm, the horizontal displacement of the 5m parts of the outer sides of the slope feet is 7.2 cm, and the calculation result is more consistent with the detection result.
Example two
In this embodiment, a natural foundation model of a railway double-track subgrade is taken as an example, and the situation of the natural foundation in the method for calculating foundation deformation based on numerical model stress extraction of the present invention is described.
The main difference between the natural foundation calculation and the composite foundation calculation in the first embodiment is that:
and S1, a natural foundation model is established, a pile plate structure (namely a pile and a concrete slab) part is not required to be established, and related contact is not required to be set.
S2, based on the natural foundation model established in the S1, after the first ground stress balance is performed, the pipe pile and the concrete slab can be directly activated without activating the pipe pile and the concrete slab by a method of a dead unit, and the embankment and the corresponding load can be directly activated; the calculated depth determination criteria are the same as the composite foundation, but the values of the calculated depth may vary due to the absence of pile effects.
And S3, directly calculating the vertical settlement of the foundation by the formula (1) without distinguishing a reinforcing area from a lower lying layer.
And S4, the method is the same as the composite foundation calculation method.
Claims (10)
1. The foundation deformation calculation method based on the numerical model stress extraction is characterized by comprising the following steps of:
s1, establishing a numerical simulation model according to an on-site working point:
establishing a numerical simulation model by using soil parameters directly acquired from a geological survey report; after material attribute setting, load setting, contact setting and boundary setting are carried out in the model, shielding units except for foundation soil by a method of a dead unit to obtain a foundation model;
s2, extracting horizontal and vertical additional stress distribution of the foundation:
the ground stress distribution under the dead weight load is calculated through a static general analysis step, and the calculated ground stress distribution is led into a foundation model obtained in S1 through an ODB file leading method to perform ground stress balance;
when the site foundation is a natural foundation, activating the embankment and the external load on the embankment in the model after the ground stress is balanced;
when the site foundation is a composite foundation, firstly activating a pile, a cushion layer or a concrete slab structure in a model after the ground stress is balanced, then carrying out ground stress balance again, and finally activating the embankment and the external load on the embankment;
extracting uniform load curve of horizontal additional stress changing along with depth by using model after external load is activatedAnd a vertical additional stress profile with depth;
s3, calculating the vertical settlement of the foundation:
calculating the vertical settlement of the foundation according to the following formula：
，
In the method, in the process of the invention,the total settlement of the foundation; />Calculating an empirical coefficient for sedimentation;
s4, calculating the horizontal displacement of the foundation:
taking a vertical soil column of a point to be measured below a ground surface projection point as an elastic foundation beam with a limited length, and taking a deflection differential equation calculated by a Winker elastic foundation beam theory as a basis;
for any position on the elastic foundation beamuUniformly distributed load applied to the position, and the uniformly distributed load is scattered into a plurality of concentrated loads by using a differential principleCalculating the horizontal displacement +.>：
，
Wherein:is the flexibility coefficient of the elastic foundation beam, +.>；/>Modulus for elastic foundation beams; />Is the section moment of inertia; />Is the width of the section; />Is the foundation bed coefficient;F 1 ，F 2 ，F 3 ，F 4 as a function of gram Lei Luofu;
；
；
；
；
the horizontal deformation of the point to be measured at the projection point of the ground surface is obtained; />The corner of the projection point of the to-be-measured point on the ground surface is the corner of the projection point of the to-be-measured point on the ground surface;the bending moment of the point to be measured at the projection point of the ground surface is the bending moment of the point to be measured at the projection point of the ground surface; />The concentrated force of the point to be measured on the projection point of the ground surface is obtained;xandythe X axis is depth, and the Y axis is horizontal deformation of the elastic foundation beam;
each length direction of the elastic foundation Liang Yanliangm divides a micro-segment into the following formula:
，
in the method, in the process of the invention,uniform load curve obtained for S2 +.>At the position ofuA value at;
function of displacement of beam with depth caused by each concentrated loadAdding, calculating any position on the beam under the action of uniformly distributed load by the following methodxHorizontal displacement of the part->：
。
2. The method according to claim 1, characterized in that: when the foundation described in S3 is a natural foundation, the total settlement amount of the foundation is calculated by the following formula：
，
Wherein:ncalculating the number of soil layers divided in the depth range for foundation settlement;is the firstiAverage compression modulus of layer soil; />Is the firstiThe thickness of the layer soil; />Is the first in the natural foundationiAverage vertical additional stress of the layer soil.
3. The method according to claim 1, characterized in that: when the foundation described in S3 is a composite foundation, the total settlement of the foundation is calculated by the following equation：
,
In the method, in the process of the invention,the settlement amount of soil mass in the reinforced area; />Is the settlement of the soil body of the lower lying layer;
order theFor the number of soil layers divided in the area of the reinforcement zone, < >>For the number of soil layers divided in the lower lying rangeSaid->Obtained by the following formula:
，
in the method, in the process of the invention,is the firstiAverage compression modulus of the layer soil; />Is the firstiThe thickness of the layer soil; />The average vertical additional stress of the i-th layer soil in the composite foundation is obtained.
4. A method according to claim 3, characterized in that: when the composite foundation is a flexible pile composite foundation, the following formula is adopted:
，
in the method, in the process of the invention,the average compression modulus of the i-th layer composite soil body of the reinforced area.
5. The method according to claim 4, wherein: calculating the said by substitution rate complex modulus methodThere is a formula:
，
，
in the method, in the process of the invention,the replacement rate is the composite foundation area; />Is the area of a single pile; />The area of the soil body unit is compounded around the pile; />Is the compression modulus of the pile body.
6. The method according to claim 4, wherein: calculation of the bearing force ratio by the composite modulus methodThere is a formula:
，
，
in the method, in the process of the invention,the foundation is the basic bearing capacity of the natural foundation; />The bearing capacity is allowed for the composite foundation; />To increase the coefficient of load bearing than compression modulus.
7. A method according to claim 3, characterized in that: when the composite foundation is a rigid pile composite foundation and the differential settlement of pile soil on the surface of the foundation is not negligible, calculating the settlement of the soil body of the reinforced area by a pile body compression methodThere is a formula:
，
in the method, in the process of the invention,the pile body penetration amount is as follows; />The compression amount of the pile body is;
compression amount of pile bodyObtained by the following formula:
，
in the method, in the process of the invention,the pile length is the pile length; />The modulus of the pile body obtained in the step S1; />The vertical additional stress is a change curve of the vertical additional stress along with the depth, and is obtained through S2 calculation; z is the depth of the pile body.
8. A method according to claim 3, characterized in that: when the composite foundation is a rigid pile composite foundation and differential settlement of pile soil on the surface of the foundation can be ignored, calculating the vertical settlement of the foundation by using a Mindlin method。
9. The method according to claim 1, characterized in that: s4, the cross section of the soil column is square, and the side length of the square is less than or equal to 0.1m; the saidLess than or equal to 0.1m, parameter->Determined by known loading conditions and boundary conditions.
10. The method according to claim 1, characterized in that: the boundary in the S1 is set to limit the horizontal displacement of the boundary surface around the model to be zero and limit the vertical displacement of the bottom edge interface to be zero; the load in S1 is set to be downward gravity acceleration; the soil property parameters comprise the gravity, the elastic modulus, the cohesive force and the internal friction angle, and the elastic modulus value is in the range of 2-5 times of the compression modulus according to engineering experience.
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